1. Field of the Invention
The present invention relates to an X-ray-tomographic imaging apparatus, an X-ray-tomographic imaging method, and a program.
2. Description of the Related Art
Hitherto, X-ray-tomographic imaging has been performed by using an X-ray film. Typically, a subject is placed between an X-ray tube and the X-ray film. X-ray exposure is performed a plurality of times while the X-ray tube and the X-ray film are moved in opposite directions, with respect to the subject, in synchronization, so that the center of the X-ray beam and the center of the X-ray film are aligned. Subsequently, an X-ray-transmission image is obtained each time the X-ray exposure is performed. Further, multiple exposures of the X-ray-transmission images are performed on one film, whereby the image of a tomographic section of the subject is obtained. In this tomographic-section image, constitutional elements of the subject at a predetermined distance from the tomographic section become blurred.
Further, digital-tomographic imaging apparatuses have been commercially introduced. In this case, the addition of a predetermined item of digital image data to another predetermined item of the digital image data is performed by using an image intensifier (hereinafter referred to as an I.I.) and a TV-imaging system that are used in place of the X-ray film. Subsequently, a reorganized image is obtained. This reorganized image is equivalent to the above-described tomographic-section image obtained in the case where the multiple exposures are performed on the film.
Japanese Patent Laid-Open No. 7-171142 discloses a radiodiagnostic device, including a solid-image pickup element that can perform non-destructive reading. This radiodiagnostic device can stop X-ray exposure based on the pixel value of an image obtained by the non-destructive reading. Further, the radiodiagnostic device can read image information after the X-ray exposure is stopped, because the image information has been accumulated in the solid-image pickup element.
Japanese Patent No. 2610438 discloses a method of driving a solid-image pickup device, including an image sensor that can perform non-destructive reading. This solid-image pickup device removes fixed-pattern noise through the non-destructive reading.
In the past, in the case where known analog imaging is performed by using an X-ray film as an image-pickup system, the X-ray tube and the X-ray film move in a predetermined orbit in a predetermined range. That is to say, the range in which the X-ray tube and X-ray film move is already determined before the tomographic imaging is performed. Therefore, if a user wishes to obtain a tomographic image in a different moving range, the user has to perform tomographic imaging again. In this case, it is impossible for the user to observe an obtained tomographic image soon after the imaging is finished.
Further, in the case where known digital-tomographic imaging is performed by using the I.I. and a TV-image-pickup system as the image-pickup system, it becomes possible to reorganize a tomographic image by using predetermined parts of the image data after the digital-tomographic imaging is finished. In this case, the predetermined part of the image data corresponds to a predetermined part of the range in which the X-ray tube and the image-pickup system move in a predetermined orbit. In this case, however, it must be arranged so that calculation is performed as many times as the number of items of image data required for the reorganization. Therefore, it is impossible to display the reorganized tomographic image soon after the tomographic imaging is finished. Further, since the tomographic imaging is performed a plurality of times in sequence, image information of a previous frame (electrical charges) often affects image information of the next frame, whereby the quality of the reorganized tomographic image is deteriorated. Further, it must be arranged so that all the data on a plurality of images obtained by the tomographic imaging is stored for the tomographic-image reorganization. Therefore, very large frame-memory capacity is required.